This invention relates in general to feed attachments for machine tools and deals more particularly with an improved bar puller for a numerically controller turret lathe or the like. In a machine of the aforedescribed general type, a plurality of tools mounted at angularly spaced tool stations on a rotary turret are sequentially indexed into working position to perform a series of turning and/or boring operations on a piece of bar stock held by a rotating chuck in response to command signals received by the machine from a programmable controller. Upon completion of a workpiece, a cut-off tool mounted at one of the tool stations moves into cutting engagement with the bar to sever the finished workpiece from the bar leaving an end portion of the bar projecting from the chuck. Thereafter, a bar puller, mounted on the turret at one of the work stations, is moved by the turret into gripping engagement with the projecting end of the bar. The chuck is then released, in accordance with a predetermined program, and the turret backs away from the chuck pulling a length of bar stock into working position in preparation for the next machine cycle.
One type of bar puller adapted for attachment to a turret includes mechanism for closing and opening jaws to grip and release a bar. Although bar pullers of the latter type are generally satisfactory for most purposes, such bar pullers are quite expensive to manufacture, install and maintain. Another type of bar puller presently in use has a resilient generally C-shaped frame which includes a pair of integral, spaced apart jaw holders. A pair of jaw pads mounted in spaced relation to each other on the jaw holders have opposing jaw surfaces for gripping a bar. The spacing between the jaw surfaces is somewhat less than the width of the bar with which the bar puller is to be used to allow for forceable insertion of the bar between the jaws. The jaws are biased into holding position by the resilient jaw holders to grip the bar. Such a bar puller may be adapted to receive a plurality of different bars in a limited range of sizes by changing jaw pads and/or inserting shims between the jaw pads and the jaw holders to vary the spacing between the jaw surfaces. The hardened jaw pads used with such bar pullers are relatively expensive. Several sets of pads may be required to adapt such a bar puller to accommodate even a limited range of bar sizes. If a significant difference exists between the sizes of bars to be processed on the machine, several such bar pullers of varying size may be required, which adds substantially to the cost of tooling.
It is the general aim of the present invention to provide an improved bar puller which does not require an operating mechanism for opening and closing its jaws and which may be readily adjusted to accommodate bars in a wide range of sizes.